User blog:Hurricane Layten/Cascadia threat increasing
OK, i know i havent edited here for a while, but i have been busy on another wiki. Anyway, thats not the point to this post... This evening,there was a series of M4-5 earthquakes on the northern end of the Cascadia Subduction Zone (CSZ), which is a little concerning, because this much activity along the megathrust is unusual. In the last blog i posted back in September, i noted the potential link between large earthquakes on Cascadia and the San Andreas system. If you werent around then, ill briefly explain it now. Looking back inot the past, there appears to bea direct link between large earthquakes on both faults. The San Andreas system has a magnitude 8 earthquaje once every 300 years on average, which is roughly the same (in geologic terms) to the 280 year return period for the Cascadia Megathrust. Check my other post for more on that subject. Seeing a magnitude 5.1 earthquakefollowed by magnitude 4.6 and 4.3 aftershocks cant be a good sign. However, there appears to be good news coming out of it, with the event happening on the more active northern section off the coast of British Colombia. Clearly there cant be much strainhaving built up since the 2001 magnitude 7.2 earthquake, so this isnt anything to worry about, right? OK, this is where it gets toally bizzare now. A magnitude 3.2 earthquake was recorded on the southern section of the megathrust just 14 hours prior to the event, which could have been a foreshock to the magnitude 5.1 event further north. This, from a scientific point of veiw, raises concern, especially when the middle section of the fault bucked in a 4.7 earthquake event back in September, which caused a magnitude 5.6 event on teh San Andreas system 3 days later, but thats not the point. The point is, the earthquakeactivity is on the rise, and comes after the end of the latest slow earthquake event. A slow earthquake event is a 14 month reverse movement of the fault along the subduction zone, which is currently not very well understood, but scientists are pretty sure what happens during the event. As the megathrust reverses its direction of movement, it adds pressure to the megathrust at a depthof about 200 km, adding to the strain of the main subduction zone, which increases the risk of the feared magnitude 9 event. I am not a trained seismologist, but i have a pretty good understanding of the processes happening at the zone. After each event, small aftershocks have been propogating along the subduction zone, which mostly seem to be missing the central section of the zone, which raises the question, what next? Well, with the central and southern sections being a seismic gap, it raises concern, because it means that the strain is potentially reaching a critical point along the subduction plane, making the area more prone to a very large earthquake (M8+). This is not the full potential of the zone, as i have said already, but it is an ominous sign of things to come, because tracking the intervals of the earthquakes, there is an average return period for a magnitude 8.5+ (megathrust) event of about 243.3 years, and the last earthquake was exactly 317 years ago today. This doesnt exactly mean anything, becasue Cascadia can have return period as short as 120 years, or as long as 2200 years, which makes the forecast difficult to place. However, having monitored the behaviour of teh fault for the last few years now, it appears that the bigger earthquakes are becoming more common, which maybe a sign of things to come in the near future. The latest slow earthquake event has been less pronounced than those of recent years, which potentially shows the breaking point of the subduction zone is near. However, saying if the event will be a megathrust is difficult to say. At current rates, there could be a magnitude 8.5 earthquake within the next 10 years, and if this carries on (i will continue to monitor), we could have the big 9 within teh next 30 years easily, and if you live along the Pacific Northwest, im pretty sure you know the numbers already. Tsunami waves of 45 feet along tight coasts, a death toll of 10000-22000, and billions of Dollars worth of damage, as well as being cut off from the outside world for up to a year following the event. If i was to take an attempt at forecasting for the great earthquake, id say there is a 10% chance of a megathrust occurring within the next 10 years, a 30% chance within the next 35 years, and a 55% chance of one within teh next 50 years. In terms of teh magnitude 9 event, id say there is a 3$ chance of this occurring within 10 years, a 20%chance within 30 years, and a 45% chance of this happening within the next 50 years. This is not a series of numbers to be relied on, because for all we all know, the earthquake could hit in a day, a year, a century, maybe even another 1000 years from now. One thing can be said about all of this though. A tsunami will travel across the Pacific when the event occurs, potentially killing tens of thousands of people along the Pacific Coasts, and this is not a topic that can be avoided, because the less vigilant people are about the immediate answer to this, the more likely they will be to perish when the big one comes. I will be monitoring the situation very closely, becausse i have a very bad feeling that the next big one is just around the corner for those in harms way, and if i am right- IF- this is the time to prepare if you havent already, becauue its the people who are unprepared that lose their lives in every disaster around the world, and 3 magnitude 5 events in the last 6 months cannot be ignored. Call me an alarmist or whatever, but when it comes to these sorts of things, i follow my hunch and usually hit the jackpot as my reward for paying close attention. Pay attention to any new data cooming in from the probes, check up the activity of the zone every once in a while if you are at risk, and dont let down your guard, because the this thing could happen at any time. Category:Blog posts